Phase-comparison carrier-current relay



Jan. 30, 1951 s. l.. GoLDsBoRouGl-l ET Al. 2,539,416

PHASE-COMPARISON CARRIER-CURRENT RELAY Filed NOV. 28, 1947 3 ap IFP e. 0u INVENTORS Shirley LlGo/dsborough and John L. lac/(burn C ....\b I

F? .5. ZMH

ATTORN EY Patented JanQBO, 1951 PHASE -COMPARISN CARRIER-CURRENT RELAY Shirley L. G-oidsborongh, Basking Ridge, and John L. Blackburn, East range, N. J., assignors to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania ppiication November 28, 1947, Serial No. 788,581

maints.

Our invention relates to the application of a phase-comparing carrier-current relaying-system to the control of single-pole breakers, using either selective-pole or single-pole tripping.

A phase-comparison carrier-current relayingsystem is a system for the protection of a linesection of a transmission-line, by transmitting carrier on alternate half-cycles oi the line-current, and thereby comparing the relative phases of the two terminal line-currents, in order to determine the existence of a fault somewhere within the ccniines of the protected line-section. Heretoiore, a response of a phase-comparison carrier-current relay-apparatus has been use to initiate the gang-tripping of all three poles of a line-sectionaiizing circuit-breaker. EX- amples of such a system are shop/'1- in the Lensner Patent 2,406,615, granted August 27, 1946, the Mehring et al. Patent 2,408,863, granted September 24, 1946, and a copending Lensner et al. application, Serial No. 753,290, filed June 30, 1947.

A selective-pole tripping-system is a protective relaying-system for controlling the several individual circuit-breaker poles, and characterized by opening only the minimum number of breakers necessary to clear a fault, an example of this kind of tripping-system being described and claimed in a Goldsborough application, Serial No. 569,181, led December 2l', 1944, patented February 22, 1949, No. 2,462,179.

A single-pole tripping-system is a protective systen?` in which single-pole breaker-operation is obtained only in the event of a single line-toground fault, and in which three-pole breakeroperation is provided for all faults between phases, an example of this kind of trippingsystem being shown in the Gcldsborough Patent 2,320,861, granted June 1, i943.

Both selective-pole and single-pole trippingsystems have heretofore used supervision by a distance-type carrier-current protective system, using individual phase-fault and ground-fault distance-responsive and directionally responsive relays, one of each kind for each phase, for detecting a fault within the protected line-section, and checking that information against similar information received from the far end of the protected line-section, in order to be able to detect faults clear out to the far end of the section, without risk of overtripping, for faults beyond the far end of the protected ine-section. Examples of such distance-type carrier-current systems are found in the Lenehan et al. Patent 2,255,934, granted September 16, 1941, the

2 Blackburn et al. Patent 2,367,921, granted January 23, 1945, and a Lenehan application, Serial No. 599,832, led June 16, 1945, patented Septomber 14, 1948, No. 2,449,490.

It is an object of our present invention to provide a simpler relaying-system for controlling single-pole circuit-breakers, using a phasecomparison carrier-current system, supplemented .by the faulty-phase phase-selectors of the G-oldsborough Patent 2,320,861, or any equivalent phase-selectors, and further supplemented by any suitable distance-responsive relays, such as are shown in the Goldsborough Patent 1,934,662, granted November 7, 1933, or the G-oldsborough Patent 2,393,983, granted February 5, 1946, or any modifications or equivalents ,.liereoi, with certain special adjustments which will be hereinafter described.

A further'object of our invention is to provide a single-pole tripping-system using a special adjustment of the trip-circle characteristics of a modified-impedance relay of the type shown in the Gol-dsborough Patent 2,393,983, whereby to avoid a response of a phase-fault distanceelement to a close-in line-to-ground fault, thereby greatly simplifying the control.

Wit-h the foregoing and other objects in view, our invention Consists in the systems, circuits, combinations, elements and methods of design and operation, which are hereinafter described and claimed, and illustrated in the accompanying drawing, wherein:

Figure l is a simplified diagrammatic view of circuits and apparatus illustrating the application of our invention in a selective-pole trippingsystem,

Fig. 2 is a similar view illustrating an application of the invention in a single-pole tripping-system,

Fig. 3 is an impedance-diagram showing the response-circle characteristic of the special phase-fault impedance-element adjustment utilized in the single-pole tripping-system of Fig. 2, and l Figs. 4 and 5 are vector diagrams showing the phase-relations of the controlling current and voltage of the same relay, for a single groundfault, and for a phase-to-phase fault, respectively.

In the drawing, We have illustrated our invention as applied to one terminal of a linesection 6 of a three-phase transmission-line, which is connected to a, three-phase stationbus l by means of three single-pole circuitbreakers CB--A, CB-B and CB-C, having trip-coils TC-A, TC-B and 'EC-(3, and each having two sets of auxiliary make-contacts oA, aA; dB, aB; and aC, aC', respectively. The line-phases are distinguished by the letters A, B and C. We have shown only one terminal of the protected line-section with the understanding that the other terminal is, or may be, a duplicate of the terminal which is illustrated in Fig. l or Fig. 2.

In Fig. l, we use a phase-fault distance-relay assembly il, which is diagrammatically indicated as a box containing t-he three phase-fault impedance-relay make-contacts ZA, ZB and ZC, for responding respectively to phase-AB faults, phase-BC faults, and phase-CA faults. These relays are suitably energized from a set of linecurrent transformers 9 and potential-transformers lll, in a known manner. The distancesettings for these impedance-elements are such that each relay has a balance-point which is just safely beyond the iai' end of the protected line-section.

In Fig. l, we also use a phase-selector assembly I2, which is symbolized by a box having three sets of make-contacts and three sets of backcontacts, marked SA, SB and SC, ior selecting the faulted phase in the event of a ground-fault. This phase-selector operation is preferably obtained by comparing the negative and zero phase-sequence components of the line-currents which are supplied to the phase-selector box lil by means of aset of line-current transformers i3, as described and claimed in the Goldsborough Patent 2,320,861.

In Fig. l, we also use a phase-comparison carrier-current relay-apparatus, which is symbolically indicated by a box lil, having a single make-contact marked ILB. This apparatus may be like that which is shown in either the Lensner Patent 2,406,615, or the Mehring et a1. Patent 2,408,868, or the Lensner et al. pending application Serial No. 758,29. It is used as a pilot-channel means for comparing the phases of the line-currents at the two ends of the protected line-section 6. It is energized by a set or linecurrent transformers i5, and it is connected, at I6, to a carrier-current coupling-capacitor il which is shown as being connected to the phase- C line-conductor, on the line-side of a carriercurrent trap i5.

While we have indicated three diferent sets of line-current transformers, ii, i3 and for convenience in schematically indicating the principles of our invention in Fig. l, it will be understood, of course, that usually only a single set of line-current transformers would be utilized to supply the relaying-currents for all three equipments, 3, i2 and ld.

In Fig. l, We have also indicated a schematic, or across-the-line, diagram of the direct-current tripping-circuits and their associated controlcircuits. rEhe various relays and switches are invariably shown in their open or deenergized positions. In each case, the main or operating coil of a relay is given a letter-designation cr legend, and the same letter-designation or legend is applied to all of the contacts of that relay. Different phases are distinguished by appropriate letters. Arrows are used to symbolically indicate how the various parts of each relay are connected together.

In the direct-current circuits of Fig. l, the phase-comparing carrier-current relaying-contact HKB is used to energize an auxiliary relaying-bus 2li from the positive lbus (-1-). This relaying-bus 2t is energized therefore, after the carrier-current equipment has determined that there is a fault, which requires tripping, in the protected line-section 5, but the carrier-current response, of the contact HKB, does not discriminate as to whether the fault is a phase-'fault or a ground-fault, or which phase or phases are affected.

In accordance with our invention as shown in Fig. l, Various relaying-circuits 2l to l are connected to the bus E, to provide the proper phaseselection and control.

The relaying-circuit 2l is a phase-A. groundfault relaying-circuit. Starting with the bus 26, it includes, in order, the SA. make-contact, the SC back-contact, and one of the three back-contacts X3 of a slugged or delayed-action relay X3, then the conductor 2i, the operating-coil CSX of an auxiliary relay CSX, the trip-circuit TA, the trip-coil TC--A of the phase-A breaker C13- A, and the auxiliary make-contact aA of the same breaker, the circuit being completed at the negative bus The CSX coil is shunted by the back-contact CSB of an auxiliary relay CSB.

The next two relaying-circuits E2 and 23 are circuits similar to the circuit 2l, which changes in the lettering for the different phases.

The next three relaying-circuits 2li, 25 and 26 are phase-fault circuits, for directly tripping the respective trip-circuits TA, TB and TC, through connections 2li-A, 25B and 26C, respectively, in response to the corresponding phase-fault impedance-relay contact ZA, ZB or ZC, respectively. These circuits 2d, Z5 and 2@ are also used, respectively, to energize the respective auxiliary-relay coils CSA, CSB and CSC, through the auxiliary breaker-switches aA', aB and aC', respectively, the "circuits being completed at the negative bus The last relaying-circuit 2l, in Fig. l, is utilized to directly energize the operating-coil X3 of the auxiliary relay X3, which is symbolically shown as being provided with a slug or short-circuiting washer 2t for introducing a small time-delay in the picking up and dropping out of this relay. The purpose of the slugged or time-delayed action of the relay X3, with its three back-contacts in the ground-fault relaying-circuits 2l, 22 and 23, is to prevent incorrect tripping when the fault-clearing breaker opens, and one of the phase-sequence selector-relays SA, SB and SC has a momentary incorrect response due to the linecurrent transient.

In accordance with our invention as shown in Fig. l, each of the auxiliary relays CSX, CSY and CSZ is provided with two correspondingly lettered make-contacts, which are used to join together all three of the rst three relaying-circuits 2 l, 22 and 23, whenever any one or" these auxiliary relays is energized. Each of the operating-coils CSX, CSY and CSZ has so much impedance that the corresponding trip-circuit TA, TB or TC does not receive an eifective or adequate tripping-current, through the coils CSX, CSY or CSZ, when that coil is placed in circuit by the opening of the shunt-connected back-contacts CSB, CSC or CSA, respectively.

The tripping-sequence of the apparatus shown in Fig. l is as follows:

In the event of a single phase-to-ground fault, say on the line-conductor A, the phase-A tripcircuit TA is energized throughthe HEB contact and the make-contact of the SA phase-selector, which picks up in response to the phase-A fault, All of the other contacts of the phase-A tripping- D circuit Z-TA are already closed', at theY time when the make-contacts HKB and SA close. If one of the impedance-contacts, or instance the phase-fault Contact ZA, should close, in response to a phase-A ground-fault very close to the relaying-switch, it would merely establish another tripping-path to the same trip-circuit TA, so that only the phase-A breaker CB-A would be tripped. The phase-fault impedance-contact ZA Would also energize the corresponding auxiliary relay CSA, causing its back-contact to` remove the short-circuit around the CSZ coil n the circuit 23, but nothing else would happen because this circuit 23 is openat the-malze-contact of the SC phase-selector, which does not respond to a phase-A line-to-ground fault.

I-n the event of a phase-to-phase iault, for example a fault between the phases B and C, the phase-fault relay-contact ZB would close, thusy tripping the phase-B breaker CB-B No response would be obtained by the phase-selector elements SA, SB and SC, because there isno zero-sequence current for a phase-to-phase fault.

InV the event oi a tWo-phase-to-ground fault, such as a fault from BA toY C to ground, the ZB contact closes, as it should do, but the phase-A selector SA also erroneously responds, as explained in the Goldsborough Patent 2,326,861. The ZB. contact trips the phase-B circuitbreaker, and it also energizes the auxiliary relay CSB, which opens.v its. back-contact CSB, thus allowing the CSX. coil to be energized in they phase-A tripping-circuitA through the Il" make-contact, thev SA make-contact, and thev SC and X3 back-contacts in the. circuit, 2i.. does, notv immediately trip. the phase-A trippingcncuit TA, because ofthe high impedance of the CSX coil, but the CSX relay picks up, and. its two make-contacts CSX short-circuit all three or" the relaying-circuits 2|, 22. and 23, thus energizing all three trip-circuits except the phase-A tripping-circuit 2I-TA, which is kept open by the open back-contact CSB. The phase-C trippingcircuit TC is energized, for example, through the I-IKB make-contact,` the contacts SA, SC and X3 in the circuit 2|, and the CSX contact to the circuit 23, continuing through the CSA back-contact to the trip-circuit TC. Thus the two proper circuit-breakers CB-B and CB-C are tripped, in the event of a double ground-fault aiecting phases B and C.

In the event of a three-phase fault, all three breakers are tripped, through the three phasefault impedance-relay contacts ZA, ZB and ZC.

In Fig. 2, we show our invention applied in a single-pole tripping-system, and this system also includes a novel feature involving the use of triply adjustable modied-impedance relays of the type shown in the G-oldsborough TPatent 2, 393,983. Thus, in Fig. 2, instead of using the impedance-relay box or panel 8 of Fig. 1, We utilize a box or panel 3i of rnodiiied-iinpedance relays, having contacts which are designatedas ZM-A, ZM-B and ZM-C, respectively. The significant thing about a modified-impedance relay is that its characteristic response-circle, instead of having its center` at the origin, as in a true impedance-relay, has its circle-center displaced from the origin in any direction and by any amount, according to the adjustments which are provided on the relay, reference being made to theA response-circle which is obtained when the pick-up value of the impedance to which the relay responds. at its balance-point, is plotted ThisV against the line-resistance R. and the 'line-i ductance X, for all possible phases of the linecurrent, throughout the entire 360 phase-shift. In other respects, the alternating-currentv connections and the alternating-current apparatus of Fig. 2 are similar to those. in Fig. l, and need no further description.

The direct-current connections in Fig. 2 are somewhat different from those in Fig. 1. They involve the same HKB Contact for energizing the relaying-bus 2G. Its three ground-fault phaseselector circuits i, 22 and 23 are much sirnpler than in Fig. 1, in that each of the circuits.

2l', 22 and 23 of Fig. 2 includes only one selector-relay Contact, namely the maire-contact for its particular selector, SA, SB or SC, as the case may be, in series with one of the three X3 backcontacts, and nothing else.

Fig. 2 does not utilize the phase-fault trippingcircuits 2'3, 25 and 2E of Fig. 1, but instead, uses circuits 24', 25 and 25 each of which contains only a single contact, that Contact being one of the three make-contacts MG or" a gang-tripping auxiliary relay MG. These relay-circuitsv 213', 25 and 25 directly energize the respective tripcircuits TA, TB and TC from the relaying-bus 23. The auxiliary switches CSA, CSB and CSC of Fig. i are not used in Fig. 2.

In Fig. 2, a triply energized relaying-circuit 33 is utilized, which is energized from the relayingbus 2Q through the three parallel-connected contacts ZM-A, ZM-B and ZMC of the modied impedance-relays. The circuit 32 energize-s the operating-coil MG of the gang-tripping relay MG, so as to trip al1 three circuit-breakers whenever there is a phase-fault response of any one of the elements ZlVi-A, ZM-B or ZM-C.

In the op ation of the Fig. 2 it will be noted that a single-phase ground-fault will pick. the proper one of the three phase-selectors SA, SB or SC. as the case be, thus resulting in a single-pcie 'oreal-:er-operation, or the tripping of a single one or" the three single-pole circuitbreakers CB A, CB-B CB-C Any other kind of fault will involve rnore than one phase of the line-condiv tripping-operation, or a tripping of all three of the oreal-zere, as a result of the response of any of the phase-fault elements Zivi-A, 21M- E or Zivi-C, energizing the master-tripping relay MG.

In the single-pole protective relaying-system f the Goldsbcroueb TBatent 2,320,861, difficulty g.- Was experienced, as explained in the patent, because of the occasional response of a phase-fault element to a close-by phase-to-ground fault, requiring a considerable amount of supervision, in order to guard against such a contingency.

In accordance with our invention, as shown in Fig. 2, we guard against the unwanted responseof a phase-fault relay to a severe single-phase ground by changing the j 1dass-fault relay fro--. a pure impedance-relay to a particular adjustment of a modified impedance-re .y, in i ich the'impedance-circle is displaced so that the relay will not respond to single-phase ground-faults, but will readily respond to the phase-to-phase fault to which it is expected to respond.

A typical phase-fault distance-relay adjustment in accordance with our inventi" i is shown in Fig. 3, wherein the circle represents the response-characteristic oi one of our modified-iinpedance relays, such as the ZM-A relay. It will be noted that the circle-center ries in the and is displaced to the right from the origin. O.

tors, and will result a gang` This phase-A modified-impedance relay is commonly limpressed with the phase-AB current (Ia-Ib) and with the phase-AB voltage (Ea-Eb). The derived line-voltage E=(Ea-Et) lies in the R-aXis in Fig. 3. The derived fault-current, for a phase-AB phase-fault, lags the voltage E by 60, and thus the relay sees a 60 lagging impedance ZFP, as indicated in Fig. 3. For a phase-A ground-fault, hovve the fault-current lags the voltage E by 120, and produces the effect of a 120 lagging impedance ZFG, as shown in Fig. 3.

Heretofore, in systems using pure impedancerelays, with the circle-center at the origin, a severe phase-A fault, with its impedance lying in the line ZFG in Fig. 3, has had a small enough appareht impedance to fall Within the response-circle characteristic of the phase-AB phase-fault iinpedance-relay. In accordance with our invention, a modified-impedance relay ZM-A is used, in which the circle-center is displaced in such a direction that the ohm-response of the relay is very small in the direction of the ohm-vector Zinc for phase-A ground-faults, While the relay has the required ohm-response reach to respond to phase-AB faults having an ohm-vector lying in the line Zep.

The relative angles of the currents and voltages, as seen by a phase-AB relay, are shown in Figs. i and 5, for a 60-line. In these iigures, the uncollapsed (or fault-free) delta line-voltages are represented by the triangles also.

Fig. 4 shows the conditions for a aero-impedance phase-A ground-fault. The line-voltages are collapsed to nbc. The impressed relay-voltage (Ea-Eb) is opposite, in phase, to the Voltage nb, as shown at EFG in Fig. fi. The phase-A ground-fault current, lagging 60 behind the collapsed line-Voltage na, is shown at Ire in Fig. li, and this is seen to be l20 behind the impressed relay-voltage Eli-1G.

Fig. 5 shows the voltage and current conditions in a phase-A phase-relay, for a i'esistanceless fault across the phases A and B. The Voltagevector triangle is collapsed to on. The relayvoltage E: (Ea-Et) is a very small voltage which is in phase with the collapsed phase-A voltage n'a, so that the relay-voltage lies somewhere in the line nd in Fig. 5. The phase-AB fault-current IFP, for a phase-AB fault on a 60-line, lags 60 behind the collapsed phase-A line-voltage rna, so that the apparent fault-current which is impressed on the relay for a phase-AB phasefault is IFPza-It), which lags 60 behind the relay voltage-vector no, shown in Fig. 5.

While We have shown our invention in only two illustrative forms of embodiment, and While We have explained useful adjustments and connections for our relay-system, we wish it to be understood that many modifications may be made, by Way of additions, omissions and substitutions, without departing -from the essential spirit of our invention. 'We desire, therefore, that the appended claims shall be accorded the broadest construction consistent with their language.

We claim as our invention:

1. Fault-responsive protective relaying-means for controlling each of a plurality of single-pole circuit-interrupters in the several phase-conductors of a three-phase line, comprising a pilotchannel relaying-means for obtaining a relayoperation in response to a comparison of the phase-angle between line-currents at the opposite ends of the protected line-section, ground-fault phase-selector means for obtaining a phase-selecting relay-operation in response to line-conditioiis obtaining in the event of a line-to-ground fault, phase-fault phase-selector means for obtaining a phase-selecting relay-operation in response to line-conditions obtaining in the event of a phase-to-phase line-fault, and circuit-interrupter control-circuit means for controlling the several single-pole circuit-interrupters in joint response to said pilot-channel relayingmeansV and said ground-fault phase-selector means, and also in joint response to said pilotchannel relaying-means and said phase-iault phase-selector means.

2. 'llie invention as defined in claim 1, characterized by said phase-iauit phase-selector means including a modiiied-impeuance phasei'ault relay-means having its impedance-criaracteiistics displaced Ironi the origin oi' resistance-ancl-inuuctance coordinates in such direc- 'tion that said relay-means has a very small ohm-responsive reach at the apparent impedance-angie which is obtained ior nearby lineto-grouiid faults, While having an adequate ohmresponsive reach at the apparent impedanceangie which is obtained for piiase-to-piiase 'i'aults `pist beyond the far end oi' the protected 'linesection.

3. 'i'he invention as defined in claim 1, characterized by said phase-ramt phase-selector means including three modiiied-impedance phase-fault relaying-means for the several compinatiohs of line-to-line phase-fault phases, and a master-controller relaying means i'or controlling all three single-poie circuit-interrupters in joint response to the pilot-channel relayingmeans and any one of said modified-impedance phase-fault reiayingmeans, each of said modified-impedance phase-fault relay-means having its impedance-characteristics displaced irom the origin of resistance-and-inductance coordinates in such direction that said relay-means has a very small ohm-responsive reach at the apparent impedance-angle which is obtained for nearby line-to-ground faults, While having an adequate ohm-responsive reach at the apparent impedance-angle which is obtained for phase-to-pnase faults just beyond the far end of the protected line-section.

4. Fault-'responsive protective relaying-means for controlling each of a plurality of single-pole circuit-interrupters in the several phase-conductors of a three-phase line, comprising a pilotchannel relaying-means for obtaining a faultresponsive relay-operation under the supervision of pilot-channel intelligence received from the far end of the protected line-section, groundfault phase-selector means for obtaining a phaseselecting relay-operation in response to line conditions obtaining in the event of a line-to-ground fault, phase-fault phase-selector means for obtaining a phase-selecting relay-operation in response to line-conditions obtaining in the event of a phase-to-phase line-fault, said phase-fault phase-selector means including a single modi-- lied-impedance phase-fault relay-element having its impedance-characteristic displaced from the origin of resistance-and-inductance coordinates in such direction that said relay-element has a very small ohm-responsive reach at the apparent impedance-angle which is obtained for nearby line-to-ground faults, While having an adequate ohm-responsive reach at the apparent impedance-angle Which is obtained for phaseto-phase faults just beyond the far end of the protected line-section, and circuit-interrupter control-circuit means for controlling the several single-pole circuit-interrupters in joint response to said pilot-channel relaying-means and said ground-fault phase-selector means, and also in joint response to said pilot-channel relayingmeans and said phase-fault phase-selector means.

5. Fault-responsive protective relaying-means for controlling each of a plurality of single-pole circuit-interrupters in the several phase-conductors of a three-phase line, comprising a pilotchannel relaying-means for obtaining a faultresponsive relay-operation under the supervision of pilot-channel intelligence received from the far end of the protected line-section, groundfault phase-selector means for obtaining a phaseselecting relay-operation in response to lineconditions obtaining in the event of a line-toground fault, phase-fault phase-selector means for obtaining a phase-selecting relay-operation in response to line-conditions obtaining in the event of a phase-to-phase line-fault, said phasefault phase-selector means including three modilied-impedanoe phase-fault relaying-elements for the several combinations of line-to-line phase-fault phases, a master-controller relaying means for controlling all three single-pole circuit-interrupters in joint response to the pilot-channel relaying means and any one of said modified-impedance phase-fault relaying elements, and circuit-interrupter control-circuit means for controlling the several single-pole circuit-interrupters in joint response to said pilot-channel relaying-means and said groundfault phase-selector means, each of said modied-impedance phase-fault relay elements having its impedance-characteristic displaced from the origin of resistance-and-inductance coordinates in such direction that said relay-element has a very small ohm-responsive reach at the apparent impedance-angle which is obtained for nearby line-to-ground faults, While having an adequate ohm-responsive reach at the apparent impedance-angle which is obtained for phaseto-phase faults just beyond the far end of the protected line-section.

SHIRLEY L. GOLDSBOROUGH.

JOHN L. BLACKBURN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,255,934 Lenehan et al. Sept. 16, 1941 2,320,861 Goldsborough June 1, 1943 2,329,043 Goldsborough et a1. Sept. 7, 1943 2,372,078 Goldsborough Mar. 20, 1945 2,381,282 Harder Aug. '7, 1945 2,386,209 Goldsborough Oct. 9, 1945 2,393,983 Goldsborough Feb. 5, 1946 

